Jenner is now slowly opening up about her experience. During a recent Q&A session with fans on Twitter, the makeup mogul revealed that she gained 40 pounds while carrying her daughter, Stormi. She quickly deleted the tweet.

Recommended weight gain for pregnant women is based on each person's body and individual needs.

"The question of weight gain in pregnancy is often a point of controversy," Gaither told INSIDER. "But in general, health providers advise weight gain based on the patient's body weight at the start of pregnancy."

Generally speaking, Gaither said most women will fall into one of these pre-pregnancy weight categories and will be advised to gain weight according to their body:

Underweight: 28 to 40 pounds

Normal weight: 25 to 35 pounds

Overweight: 15 to 20 pounds

Obese: 10 to 15 pounds

Only around one-third of pregnant women (32%) gain weight within those recommended guidelines, according to the Center for Disease Control, which noted that recent studies found that 21% had gained too little weight, and 48% had gained too much.

While Jenner's 40-pound weight gain is technically within those general parameters, fan reactions ranged from awe to disbelief.

If Jenner did lose 40 pounds in one month, two experts said that could be unsafe — or even impossible.

"Losing more than 10% of your initial body weight in one month is likely not a good idea," Dr. Caroline Apovian, director of the Nutrition and Weight Management Center at Boston Medical Center, told INSIDER.

Although health recommendations always vary based on each person's body, Apovian said that "average safe weight loss" is generally considered to be one to two pounds per month.

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Dietitian Andy Bellatti told INSIDER that barring special circumstances, like bariatric surgery, losing more than 10 pounds in a month would give him pause — and that 40 pounds would likely be impossible.

"Even with pregnancy, you could see 40 pounds lost, but that would be two or three months after birth," Bellatti told INSIDER.

It's important to keep in mind, however, that it's unclear exactly how much weight Jenner has lost.

Additionally, depending on the size of the baby and the weight of the woman's amniotic fluid and placenta (which are delivered at birth), most pregnant women can lose up to 12 pounds during delivery, according to What to Expect.